The Marine Life Information Network

Temperature increase (local)

Benchmark. A 5°C increase in temperature for one month, or 2°C for one year. Further detail

Evidence

Saccorhiza polyschides has a wide geographic distribution, and can tolerate a wide range of temperatures. Sporophyte growth can occur from 3-24°C and gametophyte development from 5-25°C (Norton, 1977). Fernández (2011) however suggested that summer temperatures of >20°C sustained for longer than a period of 30 days may inhibit development and recruitment.

Desmarestiales are unusual in that they produce and accumulate sulphuric acid within intracellular vacuoles (McClintock et al., 1982; Connor et al., 2004; Gagnon et al., 2013). Seasonal increases in temperatures limit the ability of the storage vacuoles to contain the acid and release it into the surrounding environment. The continued release of acid results in progressive decolourisation, tissue degradation and mortality of Desmarestia sporophytes (Gagnon et al., 2013). Gagnon et al. (2013) exposed Desmarestia viridis samples during 30 hour salinity and temperature treatments. At 29 and 32psu (MNCR: Full Salinity scale) Desmarestia viridis was able to tolerant to changes in temperature from 5-12°C, but exposure to 18°C was lethal to sporophytes.

The geographic distribution of Saccharina latissima is determined by the 19-20°C isotherm (Müller et al., 2009). Gametophytes can develop in ≤23°C (Lüning, 1990), but the optimal temperature range for sporophyte growth is 10-15°C (Bolton & Lüning, 1982).  Bolton & Lüning (1982) experimentally observed that sporophyte growth was inhibited by 50-70% at 20°C and following 7 days at 23°C all specimens completely disintegrated. In the field, Saccharina latissima has significant regional variation in its acclimation to temperature change. For example, Gerard & Dubois (1988) observed sporophytes of Saccharina latissima which were regularly exposed to ≥20°C could tolerate these temperatures whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C. Therefore, the response of Saccharina latissima to a change in temperatures is likely to be locally variable.

Anderson et al. (2011) transplanted Saccharina latissima from the Skagerrak region, Norway an area which has experienced a 50.7-83% Saccharina latissima decline since 2002 (Moy & Christie, 2012). Since 1960-2009 sea surface temperatures in the region have regularly exceeded 20°C (the temperature at which Saccharina latissima growth is severely inhibited) and so has the number of days which remain above 20°C. Anderson et al. (2011) hypothesised that high sea temperatures were indirectly linked to Saccharina latissima deforestation in the region, causing high epiphytic loading of sporophyte fronds (estimated to cover 80 & 100% of transplanted sporophytes). High sea temperatures has been linked to the slow growth of Saccharina latissima which is likely to decrease the photosynthetic ability of, and increase the vulnerability of Saccharina latissima to epiphytic loading, bacterial and viral attacks (Anderson et al., 2011).

Desmarestiales are sensitive to high temperatures and low salinities (Gagnon et al., 2013). Desmarestiales are unusual in that they produce and accumulate sulphuric acid (H₂SO₄) within intracellular vacuoles (McClintock et al., 1982; Connor et al., 2004; Gagnon et al., 2013). Increases in temperatures and low salinities limit the ability of the storage vacuoles to contain the acid and release it into the surrounding environment. The continued release of acid results in progressive decolourisation, tissue degradation and mortality of Desmarestia sporophytes (Gagnon et al., 2013). Gagnon et al. (2013) exposed Desmarestia viridis samples during 30 hour salinity and temperature treatments, observing at 29 and 32 psu (MNCR: Full Salinity scale) Desmarestia viridis was tolerant to changes in temperature from 5-12°C, exposure to 18°C was lethal to sporophytes. Furthermore, sporophytes that had already begun the senescence phase were exposed to 10.8 ± 0.3°C and completely shed all tissue from the stipe and laterals within ca15 days, whereas those exposed to lower temperatures of 2.5± 0.1°C lasted ca30 days. Gagnon et al. (2013) also observed Desmarestia spp. degraded progressively in low salinity treatments of 26, 23 & 20 psu (<20 psu was not tested). Therefore indicating Desmarestia spp. are highly sensitive to both high temperature (12-18°C) and low salinities (<26 psu).

IR.HIR.KSed.Sac, IR.HIR.KSed.SlatSac, IR.HIR.KSed.DesFilR, and IR.HIR.KSed.XKScrR are distributed throughout the UK (Connor et al., 2004). Northern to southern Sea Surface Temperature (SST) ranges from 8-16°C in summer and 6-13°C in winter (Beszczynska-Möller & Dye, 2013).

Sensitivity assessment. Acute 5°C increases in temperature for a period of 1 month combined with high summer temperatures may exceed the threshold temperature of 18-20°C in biotopes within the south of the UK, which would likely cause mortality of Desmarestia spp., and severely limit Saccorhiza polyschides recruitment & Saccharina latissima sporophyte growth. A 2°C increase in temperature for a period of 1 year would likely result in the exceeding an 18°C temperature threshold in the south of the UK. This temperature threshold would likely result in high mortality of Desmarestia spp. Saccharina latissima which are not acclimated to similar temperatures may also experience high and rapid mortality. Resistance has been assessed as ‘None’, Resilience as ‘High’. Sensitivity has been assessed as ‘Medium’.

Temperature decrease (local)

Benchmark. A 5°C decrease in temperature for one month, or 2°C for one year. Further detail

Evidence

Demarestia spp. are a cold water adapted genus with a polar distribution, which can grow abundantly in water temperatures of ca 0.5°C (Gagnon et al., 2013).  Saccharina latissima is also widely spread throughout the Arctic and has a lower temperature threshold for sporophyte growth at 0°C (Lüning, 1990). Subtidal red algae can survive at -2°C (Lüning, 1990; Kain & Norton, 1990). These temperatures are well below that considered within this pressure benchmark. Demarestia spp. Saccharina latissima are therefore unlikely to be adversely affected by a decrease in temperature at the benchmark level.

Saccorhiza polyschides sporophyte growth can occur within a range from 3-24°C and gametophyte development within a range of 5-25°C (Norton, 1977). Norton (1977) experimentally observed that at 3-5°C gametophytes failed to develop into viable sporophytes. This temperature range also corresponds with Saccorhiza polyschides northern range edge (ca 65° 35’N, mid Norway), above which the average winter temperature is ≤4°C (U.S. Navy, 1958).

IR.HIR.KSed.Sac, IR.HIR.KSed.SlatSac, IR.HIR.KSed.DesFilR, and IR.HIR.KSed.XKScrR are distributed throughout the UK (Connor et al., 2004). Northern to southern Sea Surface Temperature (SST) ranges from 8-16°C in summer and 6-13°C in winter (Beszczynska-Möller & Dye, 2013)

Sensitivity assessment. Both long-term and acute temperature decrease 2-5°C combined with low winter temperatures could negatively affect Saccorhiza polyschides recruitment in biotopes located in the north of the UK. Resistance has been assessed as ‘Low’, resilience as ‘High’. Sensitivity has been assessed as ‘Low’.

Salinity increase (local)

Benchmark. A increase in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

Lüning (1990) suggest that kelps are stenohaline, their general tolerance to salinity as a phenotypic group covering 16-50 psu over a 24 hr period. Optimal growth probably occurring between 30-35 psu (MNCR category-Full Salinity) and growth rates are likely to be affected by periodic salinity stress. Birkett et al. (1998b) suggested that long-term increases in salinity may affect kelp growth and may result in loss of affected kelp, and therefore loss of the biotope.

Karsten (2007) tested the photosynthetic ability of Saccharina latissima under acute 2 & 5 day exposure to salinity treatments ranging from 5-60 psu. A control experiment was also carried at 34 psu (Salinity under normal marine conditions). Between 25-55 psu Saccharina latissima had high photosynthetic ability at >80% of the control levels.

Sensitivity assessment. The evidence suggests that Saccharina latissima can tolerate exposure to hypersaline conditions of ≥40‰ (MNCR full salinity range=30-40‰). Optimal salinities for other kelps are assumed to be 30-35 psu. Hypersaline tolerances for Desmarestia spp. are unknown. Resistance has been assessed as ‘Low’, resilience as ‘High’. The sensitivity of this biotope to an increase in salinity has been assessed as ‘Low’.

Salinity decrease (local)

Benchmark. A decrease in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

Saccorhiza polyschides is affected by low salinities. Norton & South (1969) observed at ≤9‰ zoospores often burst due to internal osmotic pressure and none developed. At ≤25‰,  only 25% of gametophytes germinated and at ≤20‰ sporophyte growth was often retarded. At ≤35‰, 76% of gametophytes germinated. These results demonstrate that at ≤25‰ recruitment may be inhibited and sporophyte growth retarded.

Karsten (2007) tested the photosynthetic ability of Saccharina latissima under acute 2 & 5 day exposure to salinity treatments ranging from 5-60 psu. A control experiment was also carried at 34 psu (Salinity under normal marine conditions). Between 25-55 psu Saccharina latissima had a high photosynthetic ability at >80% of the control levels. Hyposaline treatment of 10-20 psu led to a gradual decline of photosynthetic ability. After 2 days at 5 psu, Saccharina latissima s photosynthetic ability was ~30% of control. After 5 days at 5 psu, Saccharina latissima specimens became bleached and showed signs of severe damage. The experiment was conducted on Saccharina latissima from the Arctic, and the authors suggest that at extremely low water temperatures (1-5°C) macroalgae acclimation to rapid salinity changes could be slower than at temperate latitudes. It is, therefore, possible that Saccharina latissima of the UK may be able to acclimate to salinity changes more effectively and quicker.

Gagnon et al. (2013) observed Desmarestia spp. sporophytes degraded progressively in low salinity treatments of 26, 23 & 20 psu (<20 psu was not tested). Desmarestia spp. accumulate sulphuric acid throughout the growth season which is released when the sporophyte becomes stressed under high temperatures or low salinities. Acid release causes progressive degradation of the sporophyte and mortality. Gagnon et al. (2013) exposed Desmarestia viridis samples during 30 hour salinity and temperature treatments, observing Desmarestia spp. degraded progressively in low salinity treatments of 26, 23 & 20psu (<20psu was not tested).

Sensitivity assessment. A decrease in one MNCR salinity scale from “Full Salinity” (30-40psu) to “Reduced Salinity” (18-30 psu) may result in mortality of Desmarestia spp. inhibit Saccorhiza polyschides recruitment and inhibit Saccharina latissima photosynthesis. Resistance has been assessed as ‘Low’ resilience as ‘High’. The sensitivity of this biotope to a decrease in salinity has been assessed as ‘Low’.

Water flow (tidal current) changes (local)

Benchmark. A change in peak mean spring bed flow velocity of between 0.1 m/s to 0.2 m/s for more than one year. Further detail

Evidence

Peteiro & Freire (2013) measured Saccharina latissima growth from 2 sites, the 1^st had maximal water velocities of 0.3 m/sec and the 2^nd 0.1 m/sec. At site 1 Saccharina latissima had significantly larger biomass than at site 2 (16kg /m to 12 kg /m respectively). Peteiro & Freire (2013) suggested that faster water velocities were beneficial to Saccharina latissima growth. However, Gerard & Mann (1979) measured Saccharina latissima productivity at greater water velocities and found Saccharina latissima productivity is reduced in moderately strong tidal streams (≤1m/sec) when compared to weak tidal streams (<0.5m/sec).

IR.HIR.KSed.SlatSac can be found from very strong (>3m/sec) to very weak tidal streams. IR.HIR.KSed.Sac, IR.HIR.KSed.DesFilR, IR.HIR.KSed.XKScrR can be found from moderately strong (0.5-1.5m/sec) to weak tidal streams (0.5m/sec). An increase in tidal flow may increase local sediment mobility and scour, potentially increasing dislodgment of kelps (Birket et al., 1998) and Desmarestia spp.

Sensitivity assessment. Due to the range of tidal streams which these biotopes can be found a change of 0.1m/s to 0.2m/s, is not likely to dramatically affect biotope structure. Resistance has been assessed as ‘High’, resilience as ‘High’. Sensitivity has been assessed as ‘Not Sensitive’.

Emergence regime changes

Benchmark.  1) A change in the time covered or not covered by the sea for a period of ≥1 year or 2) an increase in relative sea level or decrease in high water level for ≥1 year. Further detail

Evidence

IR.HIR.KSed.Sac and IR.HIR.KSed.XKScr can be found on sublittoral fringe rock so that the characterizing species would be exposed during low spring tides. IR.HIR.KSed.SlatSac and IR.HIR.KSed.DesFilR are found in the infralittoral and as such would only be exposed on extreme low tides (Connor et al., 2004).

An increase in emergence will result in an increased risk of desiccation and mortality of the dominant seaweeds (Desmarestia spp., Saccorhiza polyschides, Saccharina latissima). Removal of canopy forming seaweeds has also been shown to increase desiccation and mortality of the understorey macroalgae (Hawkins & Harkin, 1985). Providing that suitable substrata are present, the biotope is likely to re-establish further down the shore within a similar emergence regime to that which existed previously.  A decrease in emergence could, however, result in  an extension of the biotope further up the shore, although its lower limit is still probably controlled by light penetration, competition and grazing so that entire extent of the biotope may  move.

Sensitivity assessment. Resistance has been assessed as ‘Low’. Resilience as ‘High’. The sensitivity of this biotope to a change in emergence is considered as ‘Low’.

Wave exposure changes (local)

Benchmark. A change in near shore significant wave height of >3% but <5% for more than one year. Further detail

Evidence

IR.HIR.KSed.Sac, IR.HIR.KSed.SlatSac, IR.HIR.KSed.DesFilR, IR.HIR.KSed.XKScrR are recorded from extremely exposed to wave sheltered sites and characterized by rapidly colonising macro-algae (Connor et al., 2004). As a result of rapid recovery, the community is relatively resistant to disturbance when compared to other kelp biotopes (e.g. IR.HIR.Kfar.LhypR). Birkett et al. (1998b) suggest that Saccharina latissima and Saccorhiza polyschides are rarely present in areas of wave exposure, where they may be spatially out-competed by Laminaria hyperborea.  However, the seasonally unstable nature of the substrata or periodic sediment scour within theses biotopes is likely to inhibit the growth of long lived species, such as Laminaria hyperborea and allow opportunistic species such as Demarestia spp., Saccharina latissima and Saccorhiza polyschides to proliferate.  An increase in local wave height may increase local sediment mobility and scour, potentially increasing dislodgment of kelps (Birket et al., 1998) and Desmarestia spp. The biotopes may appear sparse after winter storms but the biotope recovers again due to rapid colonization and growth by the dominant kelps and Desmarestia spp.

Sensitivity assessment. The biotope is dominated by rapid colonizing species that tolerate or rapidly recover from scour, siltation and burial.  They occur across a broad wave exposure range, and, therefore, a change in nearshore significant wave height of 3-5% is not likely to have a significant effect on biotope structure. Resistance has been assessed as ’High’, resilience as ‘High’. Therefore, sensitivity has been assessed as ‘Not Sensitive’ at the benchmark level.

Transition elements & organo-metal contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed but evidence is presented where available.

Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds is: Organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. Cole et al., (1999) reported that Hg was very toxic to macrophytes. Similarly, Hopkin & Kain (1978) demonstrated sub-lethal effects of heavy metals on kelp gametophytes and sporophytes, including reduced growth and respiration. Sheppard et al. (1980) noted that increasing levels of heavy metal contamination along the west coast of Britain reduced species number and richness in holdfast fauna, except for suspension feeders which became increasingly dominant. Gastropods may be relatively tolerant of heavy metal pollution (Bryan, 1984). Although macroalgae species may not be killed, except by high levels of contamination, reduced growth rates may impair the ability of the biotope to recover from other environmental disturbances. Thompson & Burrows (1984) observed the growth of Saccharina latissima sporophyte growth was significantly inhibited at 50 µg Cu /l, 1000 µg Zn/l and 50 µg Hg/l. Zoospores were found to be more intolerant and significant reductions in survival rates were observed at 25 µg Cu/l, 1000 µg Zn/l and 5 µg/l.

Hydrocarbon & PAH contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed but evidence is presented where available.

IR.HIR.KSed.Sac, IR.HIR.KSed.SlatSac, IR.HIR.KSed.DesFilR, IR.HIR.KSed.XKScrR, are predominantly recorded in the sub-tidal (<0 m). These habitats are therefore not likely to come into contact with freshly released oil but only to sinking emulsified oil and oil adsorbed onto particles (Birket et al., 1998b). The mucilaginous slime layer coating of laminarians may protect them from smothering by oil. Hydrocarbons in solution reduce photosynthesis and may be algicidal. However, Holt et al. (1995) reported that oil spills in the USA and from the Torrey Canyon had little effect on kelp forests. Similarly, surveys of subtidal communities at a number sites between 1-22.5m below chart datum showed no noticeable impacts of the Sea Empress oil spill and clean up (Rostron & Bunker, 1997). Laboratory studies of the effects of oil and dispersants on several red algae species, including Delesseria sanguinea (Grandy 1984; cited in Holt et al., 1995) concluded that they were all sensitive to oil/ dispersant mixtures, with little differences between adults, sporelings, diploid or haploid life stages.

Synthetic compound contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed but evidence is presented where available.

O'Brian & Dixon (1976) suggested that red algae were the most sensitive group of macrophytes to oil and dispersant contamination (see Smith, 1968). Saccharina latissima has also been found to be sensitive to antifouling compounds. Johansson (2009) exposed samples of Saccharina latissima to several antifouing compounds, observing chlorothalonil, DCOIT, dichlofluanid and tolylfluanid inhibited photosynthesis. Exposure to Chlorothalonil and tolylfluanid, was also found to continue inhibiting oxygen evolution after exposure had finished, and may cause irreversible damage.

Smith (1968) observed that epiphytic and benthic red algae were intolerant of dispersant or oil contamination during the Torrey Canyon oil spill; only the epiphytes Crytopleura ramosa and Spermothamnion repens and some tufts of Jania rubens survived together with Osmundea pinnatifida, Gigartina pistillata and Phyllophora crispa from the sublittoral fringe. Delesseria sanguinea was probably the most intolerant since it was damaged at depths of 6m (Smith, 1968). Holt et al.(1995) suggested that Delesseria sanguinea is probably generally sensitive of chemical contamination.

Radionuclide contamination

Benchmark. An increase in 10µGy/h above background levels. Further detail

Evidence

No evidence

Introduction of other substances

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed.

De-oxygenation

Benchmark. Exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for one week (a change from WFD poor status to bad status). Further detail

Evidence

Reduced oxygen concentrations can inhibit both photosynthesis and respiration in macroalgae (Kinne, 1977). Despite this, macroalgae are thought to buffer the environmental conditions of low oxygen, thereby acting as a refuge for organisms in oxygen-depleted regions especially if the oxygen depletion is short-term (Frieder et al., 2012).If levels do drop below 4 mg/l negative effects on these organisms can be expected with adverse effects occurring below 2 mg/l (Cole et al., 1999).  However, in wave exposed, highly mixed, areas, the hypoxic conditions are likely to be transient.

Sensitivity Assessment. Reduced oxygen levels are likely to inhibit photosynthesis and respiration but not cause a loss of the macroalgae population directly. Resistance has been assessed as ‘High’, and resilience as ‘High’. Sensitivity has been assessed as ‘Not sensitive’ at the benchmark level.

Nutrient enrichment

Benchmark. Compliance with WFD criteria for good status. Further detail

Evidence

Conolly & Drew (1985) found that Saccharina latissima sporophytes plants at the most eutrophic site in a study on the east coast of Scotland where nutrient levels were 25% higher than ambient levels exhibited a high growth rate. However, Read et al. (1983) reported after removal of a major sewage pollution in the Firth of Forth, Saccharina latissima became abundant where previously it had been absent. Bokn et al. (2003) conducted a nutrient loading experiment on intertidal fucoids. Within 3 years of the experiment no significant effect was observed in the communities, however, 4-5 years into the experiment a shift occurred from perennials to ephemeral algae occurred. Although Bokn et al. (2003) focussed on fucoids the results could indicate that long-term (>4 years) nutrient loading can result in community shift to ephemeral algae species, and explain the disparity between the findings of Conolly & Drew (1985) & Read et al. (1983).

Johnston & Roberts (2009) conducted a meta-analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected 6 marine habitats (including subtidal reefs). A 30-50% reduction in species diversity and richness was identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) however also highlighted that macro-algal communities are relatively tolerant to contamination, but that contaminated communities can have low diversity assemblages which are dominated by opportunistic and fast growing species (Johnston & Roberts, 2009 and references therein). Nutrient enrichment may also result in phytoplankton blooms that increase turbidity and, therefore, may negatively impact photosynthesis.

Sensitivity assessment. However, the biotope is assessed as ‘Not sensitive’ at the pressure benchmark that assumes compliance with good status as defined by the WFD.

Organic enrichment

Benchmark. A deposit of 100 gC/m²/yr. Further detail

Evidence

Conolly & Drew (1985) found Saccharina latissima sporophytes had relatively higher growth rates close to a sewage outlet in St Andrews, UK when compared to other sites along the east coast of Scotland. At St Andrews, nitrate levels were 20.22µM, which represents an approx 25% increase when compared to other comparable sites (approx 15.87 µM). Handå et al. (2013) also reported Saccharina latissima sporophytes grew approx 1% faster per day when in close proximity to Norwegian Salmon farms, where elevated ammonium can be readily absorbed.  Read et al. (1983) reported after the installation of a new sewage treatment works, which reduced the suspended solid content of liquid effluent by 60% in the Firth of Forth, Saccharina latissima became abundant where previously it had been absent. Bokn et al. (2003) conducted a nutrient loading experiment on intertidal fucoids. Within 3 years of the experiment no significant effect was observed in the communities, however, 4-5 years into the experiment a shift occurred from perennials to ephemeral algae occurred. Although Bokn et al. (2003) focussed on fucoids the results could indicate that long-term (>4 years) nutrient loading can result in community shift to ephemeral algae species. Differences between the findings of the aforementioned studies are likely to be related to the level of organic enrichment, however, could also be time dependent.

Johnston & Roberts (2009) conducted a meta-analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected 6 marine habitats (including subtidal reefs). A 30-50% reduction in species diversity and richness was identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) however also highlighted that macroalgal communities are relatively tolerant to contamination, but that contaminated communities can have low diversity assemblages which are dominated by opportunistic and fast growing species (Johnston & Roberts, 2009 and references therein). Organic enrichment may also result in phytoplankton blooms that increase turbidity and, therefore, may negatively impact photosynthesis.

Sensitivity assessment. Although short-term exposure (<4 years) to organic enrichment may not affect seaweeds directly, indirect effects such as turbidity may significantly affect photosynthesis.  Therefore, resistance has been assessed as ‘Medium’, resilience as ‘High’ and sensitivity as ’Low’.

Physical loss (to land or freshwater habitat)

Benchmark. A permanent loss of existing saline habitat within the site. Further detail

Evidence

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very Low’).  Sensitivity within the direct spatial footprint of this pressure is therefore ‘High’.  Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

Physical change (to another seabed type)

Benchmark. Permanent change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa. Further detail

Evidence

If rock substrata were replaced with sedimentary substrata this would represent a fundamental change in habitat type, which Saccharina latissima, Saccorhiza polyschides and Desmarestia spp. would not be able to tolerate. The biotope would be lost.

Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Very Low’. The sensitivity of this biotope to change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa is assessed as ‘High’.

Physical change (to another sediment type)

Benchmark. Permanent change in one Folk class (based on UK SeaMap simplified classification). Further detail

Evidence

Not relevant

Habitat structure changes - removal of substratum (extraction)

Benchmark. The extraction of substratum to 30 cm (where substratum includes sediments and soft rock but excludes hard bedrock). Further detail

Evidence

Not relevant

Abrasion / disturbance of the surface of the substratum or seabed

Benchmark. Damage to surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

Abrasion of the substratum e.g. from bottom or pot fishing gear, cable laying etc. may cause localised mobility of the substrata and mortality of the resident community. The effect would be situation dependent however if bottom fishing gear were towed over a site it may mobilise a high proportion of the rock substrata and cause high mortality in the resident community. However, the characteristic species within IR.HIR.KSed.Sac, IR.HIR.KSed.SlatSac, IR.HIR.KSed.DesFilR, and IR.HIR.KSed.XKScrR have rapid growth rates and are distinctive of “disturbed areas. Information on from experimental clearances is summarised under resilience above.

Sensitivity assessment. Resistance has been assessed as ‘None’, Resilience as ‘High’. Sensitivity has been assessed as ‘Medium’.

Penetration or disturbance of the substratum subsurface

Benchmark. Damage to sub-surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

Not relevant, please refer to pressure 'Abrasion/disturbance of the substratum on the surface of the seabed'.

Changes in suspended solids (water clarity)

Benchmark. A change in one rank on the WFD (Water Framework Directive) scale e.g. from clear to intermediate for one year. Further detail

Evidence

Suspended Particle Matter (SPM) concentration has a linear relationship with subsurface light attenuation (Kd) (Devlin et al., 1998). Light penetration influences the maximum depth at which kelp species can grow and it has been reported that laminarians grow at depths at which the light levels are reduced to 1 percent of incident light at the surface. Maximal depth distribution of laminarians, therefore, varies from 100m in the Mediterranean to only 6-7m in the silt-laden German Bight.  In Atlantic European waters, the depth limit is typically 35m. In very turbid waters the depth at which kelp is found may be reduced, or in some cases excluded completely (e.g. Severn Estuary), because of the alteration in light attenuation by suspended sediment (Lüning, 1990; Birkett et al., 1998). Limited information is available on which to assess the effect of a decrease in water clarity on Laminariales show a decrease of 50% photosynthetic activity when turbidity increases by 0.1/m (light attenuation coefficient =0.1-0.2/m; Staehr & Wernberg, 2009). Demarestia spp. recruitment has also been found to be highly affected by light attenuation and frequency, typically rare (ca <10% coverage (Edwards, 1998) beneath kelp canopies where light levels can be 1-5% of surface irradiance (Kitching, 1941).

A decrease in water clarity as a result of mobilised sediments may also increase sediment scour of biotopes within close proximity. However, the characterizing species within IR.HIR.KSed.Sac, IR.HIR.KSed.SlatSac, IR.HIR.KSed.DesFilR, and IR.HIR.KSed.XKScrR have rapid growth and colonisation rates are as such relatively resilient to sediment scouring.

Sensitivity assessment. An increase in water clarity from clear to intermediate (10-100mg/l) represent a change in light attenuation of ca 0.67-6.7 Kd/m and is likely to result in a greater than 50% reduction in photosynthesis of Laminaria spp. The biotope is typical of sediment affected habitats and laminarians occur at a lower abundance than in other HIR.KSwed biotopes. But Desmarestia recruitment and presumably growth is likely to be affected adversely by the reduction in light and the abundance of the important characterizing species could decline. Therefore, resistance to this pressure is assessed as ‘Low’. Resilience to this pressure is assessed as ‘High’ and this biotope is regarded as having a sensitivity of ‘Low‘.

Smothering and siltation rate changes (light)

Benchmark. ‘Light’ deposition of up to 5 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

Smothering by sediment e.g. 5 cm material during a discrete event, is unlikely to damage Saccharina latissima, Saccorhiza polyschides and Desmarestia spp. sporophytes but may provide a physical barrier to zoospore settlement and therefore negatively impact on recruitment processes (Moy & Christie, 2012). Laboratory studies showed that kelp and gametophytes can survive in darkness for between 6-16 months at 8°C and would probably survive smothering by a discrete event and once returned to normal conditions gametophytes resumed growth or maturation within 1 month (Dieck, 1993). Saccorhiza polyschides zoospores successfully developed after 180 days of darkness (Norton, 1977). Intolerance to this factor is likely to be higher during the peak periods of sporulation and/or spore settlement.

IR.HIR.KSed.Sac, IR.HIR.KSed.SlatSac, IR.HIR.KSed.DesFilR, IR.HIR.KSed.XKScrR are found from extreme wave exposed-sheltered sites (Connor et al., 2004). In wave exposed biotopes deposited sediment is unlikely to remain for more than a few tidal cycles (due to water flow or wave action). In sheltered biotopes deposited sediment could remain and the effects of deposition could be longer lasting.

Sensitivity assessment. Resistance has been assessed as ‘High’, resilience as ‘High’ and sensitivity as ‘Not Sensitive’.

Smothering and siltation rate changes (heavy)

Benchmark. ‘Heavy’ deposition of up to 30 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

Smothering by sediment e.g. 30 cm material during a discrete event is unlikely to damage Saccharina latissima, Saccorhiza polyschides, and Desmarestia spp. sporophytes but may provide a physical barrier to zoospore settlement and therefore negatively impact on recruitment processes (Moy & Christie, 2012). The volume of sediment may also inundate juvenile sporophytes. Given the short life expectancy of Saccharina latissima (2-4 years;Parke, 1948), self-sustaining populations are likely to be dependent on annual recruitment (Moy & Christie, 2012). Given the microscopic size of the gametophyte, 30 cm of sediment could be expected to significantly inhibit growth.  Laboratory studies showed that kelp and gametophytes can survive in darkness for between 6-16 months at 8°C and would probably survive smothering by a discrete event and once returned to normal conditions gametophytes resumed growth or maturation within 1 month (Dieck, 1993).  Saccorhiza polyschides zoospores, specifically, successfully developed after 180 days of darkness (Norton, 1977). Intolerance to this factor is likely to be higher during the peak periods of sporulation and/or spore settlement.

IR.HIR.KSed.XKScrR is subject to periodic burial from surrounding sediments, however, IR.HIR.KSed.Sac, IR.HIR.KSed.SlatSac, IR.HIR.KSed.DesFilR, and IR.HIR.KSed.XKScrR are recorded from extreme wave exposed-sheltered sites (Connor et al., 2004) and, therefore, the effects of burial are likely to be mediated. In highly wave exposed biotopes deposited sediment is unlikely to remain for more than a few tidal cycles (due to water flow or wave action). In sheltered biotopes, the high volume of deposited sediment could remain and the effects could be longer lasting. However, these biotopes are periodically disturbed by winter storms or sediment scour therefore deposited sediments are unlikely to remain for a full season.

Sensitivity assessment. Resistance has been assessed as ‘Medium’, resilience as ‘High’. Sensitivity has been assessed as ‘Low’.

Litter

Benchmark. The introduction of man-made objects able to cause physical harm (surface, water column, seafloor or strandline). Further detail

Evidence

Not assessed.

Electromagnetic changes

Benchmark. A local electric field of 1 V/m or a local magnetic field of 10 µT. Further detail

Evidence

No evidence

Underwater noise changes

Benchmark. MSFD indicator levels (SEL or peak SPL) exceeded for 20% of days in a calendar year. Further detail

Evidence

Not relevant

Introduction of light or shading

Benchmark. A change in incident light via anthropogenic means. Further detail

Evidence

There is no evidence to suggest that anthropogenic light sources would affect Saccharina latissima, Saccorhiza polyschides and Desmarestia spp. Shading of the biotope (e.g. by the construction of a pontoon, pier etc) could adversely affect the biotope in areas where the water clarity is also low, and tip the balance to shade tolerant species, resulting in the loss of the biotope directly within the shaded area, or a reduction in seaweed abundance.

Sensitivity assessment. Resistance is probably 'Low', with a 'Medium' resilience and a sensitivity of 'Medium', albeit with 'low' confidence due to the lack of direct evidence.

Barrier to species movement

Benchmark. A permanent or temporary barrier to species movement over ≥50% of water body width or a 10% change in tidal excursion. Further detail

Evidence

Not relevant. This pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit the dispersal of spores.  But spore dispersal is not considered under the pressure definition and benchmark.

Death or injury by collision

Benchmark. Injury or mortality from collisions of biota with both static or moving structures due to 0.1% of tidal volume on an average tide, passing through an artificial structure. Further detail

Evidence

Not relevant. Collision from grounding vessels is addressed under abrasion above.

Visual disturbance

Benchmark. The daily duration of transient visual cues exceeds 10% of the period of site occupancy by the feature. Further detail

Evidence

Not relevant

Genetic modification & translocation of indigenous species

Benchmark. Translocation of indigenous species or the introduction of genetically modified or genetically different populations of indigenous species that may result in changes in the genetic structure of local populations, hybridization, or change in community structure. Further detail

Evidence

At the time of writing no evidence regarding the genetic modification or effects of translocation of native kelp populations was found.

Introduction or spread of invasive non-indigenous species

Benchmark. The introduction of one or more invasive non-indigenous species (INIS). Further detail

Evidence

Competition with invasive macroalgae may be a potential threat to native kelp biotopes.  Potential invasives include Undaria pinnatifida, Sargassum muticum and Codium fragile (de Bettignies et al., 2021). In Nova Scotia, Codium fragile competes successfully with native kelps for space including Laminaria digitata, exploiting gaps within the kelp beds.  Once established, the algal mat created by Codium fragile prevents re-colonization by other macro-algae (Scheibling et al., 2006).

Sargassum muticum is a circumglobal invasive species (Engelen et al., 2015).  It is recorded (2015) from Norway to Morocco and into the Mediterranean in the eastern Atlantic and from Alaska to Baja California in the eastern Pacific and from southern Russia to southern China in the western Pacific (Engelen et al., 2015).  It colonizes a variety of habitats and can tolerate -1°C to 30°C and survive salinities below 10 ppt.  Although fertilization does not occur below 15 ppt and growth of germlings is limited below 10°C it can complete its life cycle as long as temperatures are over 8°C for at least four months of the year (Engelen et al., 2015).  However, its distribution is limited by the availability of hard substratum (e.g. stones >10 cm) and light (Staeher et al., 2000; Strong & Dring 2011; Engelen et al., 2015).  It is most abundant between 1 and 3 m below mean water.  But it has been recorded at 18 m or 30 m in the clear waters of California.  However, it is a poor competitor under low light and only develops dense canopies in shallow areas (Engelen et al., 2015).

Sargassum muticum was shown to replace and out-compete leathery, canopy-forming macroalgae such as Saccharina latissima, Halidrys siliquosa, and Fucus spp. and, to a lesser degree, understorey species such as Codium fragile, Chondrus crispus and Dictyota dichotoma in Limfjorden, Denmark between 1984 and 1997 (Staehr et al., 2000; Engelen et al., 2015; de Bettignies et al., 2021).  The invasion in Limfjorden had stabilized by 2005 although many of the native macroalgal species continued to decline (Engelen et al., 2015).  In Limfjorden, the distribution of Sargassum muticum was limited to areas with hard substratum, in particular stones >10 cm in diameter, while smaller stones, gravel and sand were unsuitable.  It was most abundant between 1 and 4 m in depth but had low cover at 0-0.5 m or 4-6 m, in the turbid waters of the Limfjorden.  Limfjorden is wave sheltered although wave exposure has been reported to restrict the growth and survival of Sargassum muticum (Staehr et al., 2000).  Viejo et al. (1995) reported that Sargassum muticum transplanted to wave exposed shores in Spain experienced >80% breakages within a month and that the growth of undamaged plants was significantly lower than that of plants on sheltered shores.  Similarly, Andrew & Viejo (1998) noted that Sargassum muticum was restricted to intertidal rockpools in wave exposed sites in the Bay of Biscay.

Experimental manipulation of subtidal algal canopies in San Juan Islands, Washington State, USA, showed that Sargassum muticum reduced the abundance and diversity of native macroalgae, including the kelp Laminaria bongardiana and Desmarestia spp. due to shading.  However, experimental removal of Sargassum resulted in the recovery of native species within about one year (Britton-Simmons, 2004; Engelen et al., 2015).  The negative effects of Sargassum muticum on native macroalgae are mainly due to completion to light, rather than changes in nutrient availability, sedimentation or water flow (Britton-Simmons, 2004; Engelen et al., 2015).

Undaria pinnatifida (Wakame or Asian kelp) is a large brown seaweed and an Invasive Non-Indigenous Species (INIS) that could out-compete native UK kelp species (see Farrell & Fletcher, 2006; Thompson & Schiel, 2012; Brodie et al., 2014; Hieser et al., 2014; Arnold et al., 2016; Epstein & Smale, 2017; Kraan, 2017; Epstein & Smale, 2018; Epstein et al., 2019a,b; Tidbury, 2020). Undaria pinnatifida originates from Japan but is established currently on the coastlines of New Zealand, Australia, Northern France, Spain, Italy, the UK, Portugal, Belgium, Holland, Argentina, Mexico, and the USA (De Leij et al., 2017). Undaria pinnatifida was first recorded in the UK in the Hamble Estuary in 1994 (Macleod et al., 2016) and has since proliferated along UK coastlines. One year after its discovery at the Queen Anne Battery marina, Plymouth, it had become a major fouling plant on pontoons (Minchin & Nunn, 2014). Although initially restricted to artificial habitats, such as marinas and ports, it is now widespread in natural habitats in several areas, including Plymouth Sound.

Undaria pinnatifida seems to settle better on artificial substrata (e.g. floats, marinas or piers) than on natural rocky shores among local kelps (Vaz-Pinto et al., 2014). It is found predominantly in low intertidal to shallow subtidal habitats (Epstein et al., 2019b) and is significantly more abundant on artificial substrata compared to natural rocky substrata (Heiser et al., 2014; Epstein & Smale, 2018). James (2017) suggested that Undaria pinnatifida could out-compete native species on artificial substrata (such as marinas and wharf structures). De Leij et al. (2017) suggested that in natural substrata, Undaria pinnatifida can be inhibited by the presence of native competitors, such as large perennial species. The species behaves as a winter annual and recruitment occurs in winter followed by rapid growth through spring, maturity and then senescence through summer, with only the microscopic life stages persisting through autumn. It exhibits multiple dispersal strategies, such as short-range spore dispersal, and long-range dispersal as whole drift plants or fragments. Undaria pinnatifida has spread rapidly across the UK and Europe, resulting in community-wide responses and impacts (Vaz-Pinto et al., 2014; Epstein & Smale, 2017). Its impacts are complex and context-specific, depending on space, time, and taxa present in the introduced location (Epstein & Smale, 2017; Teagle et al., 2017; Tidbury, 2020).

Undaria pinnatifida has been reported to both co-exist with and out-compete Saccharina latissima (Farrell & Fletcher, 2006; Heiser et al., 2014; Epstein et al., 2019b). For example, in Torquay Marina, UK, Farrell & Fletcher (2006) completed a canopy removal experiment between 1996-2002. They reported that Saccharina latissima decreased in both control and treatment plots from ca 3 plants per 0.45 m² in 1996 to ca 1 plant per 0.45 m² in 1997 and had disappeared completely from pontoons by 2002. This coincided with a significant increase in Undaria pinnatifida from 0 plants per 0.45 m² in 1996 to ca 6 plants per 0.45 m² in 1997. However, there was a slight decrease in Undaria pinnatifida at both control and treatment plots between 1997 and 1998. By 2002, Undaria pinnatifida had recovered at control and treatment plots to ca 4-6 plants per 0.45 m² whereas Saccharina latissima had not.

In Plymouth Sound (UK), Epstein et al. (2019b) found that within its depth range (+1 to –4 m), Undaria pinnatifida co-existed with seven species of canopy-forming brown macroalgae, including Saccharina latissima. However, they reported that Undaria pinnatifida biomass was negatively related to Saccharina latissima in both intertidal and subtidal habitats. This was only statistically significant in subtidal habitats, which suggested that there was some competition between the two species (Epstein et al., 2019b). Heiser et al. (2014) surveyed 17 sites within Plymouth Sound, UK and found that Saccharina latissima was significantly more abundant at sites with Undaria pinnatifida with ca 5 Saccharina latissima individuals per m² present, compared to ca 0.5 Saccharina latissima individuals per m² present at sites without Undaria pinnatifida.

Epstein et al. (2019a) reported that when Undaria pinnatifida was removed from sites in Plymouth Sound, there was no difference in understorey assemblages. Surveys revealed that there was a high variation in the abundance and mean cover of understory macroalgae, both between plots and survey months. For example, the mean cover of brown understorey algae followed the same trend for each removal treatment (0%, 50% and 100% removal of Undaria pinnatifida). Epstein et al. (2019a) observed an initial increase in mean percentage cover of brown understorey algae 0-5 months following the removal of Undaria pinnatifida, which peaked after 7 months. This then decreased 7-15 months post-removal and then slightly recovered after 16-20 months.

Sensitivity assessment.  IR.HIR.KSed.DesFilR is wave exposed and has weak to moderately strong tidal streams that result in seasonally mobile substrata, especially in winter storms. Hence, it is dominated by opportunistic annuals such as Desmarestia spp. with only stunted individual kelps such as Saccharina latissima and Laminaria hyperborea present where bedrock is available.

Undaria pinnatifida may be able to colonize the biotope although winter mobility of substrata may interfere with its recruitment.  However, it is unlikely to out-compete the native kelps in wave exposed conditions. Also, the evidence suggests that Undaria pinnatifida does not affect the abundance of brown understorey algae. Similarly, Sargassum muticum prefers wave sheltered conditions in shallow waters or the sublittoral fringe and is unlikely to out-compete the native kelps or brown algae in the wave exposed conditions and depth (5-10 m) that define this biotope.  Therefore, the presence of a few individuals of Sargassum muticum and/or Undaria pinnatifida is unlikely to have a significant effect on the community of the biotope. Hence, resistance is assessed as ‘Medium’ to represent their potential to replace individuals of the characteristic native kelps but this is a precautionary assessment. Resilience is assessed as ‘High’ as the biotope is disturbed and both the native and non-native species need to recolonize and/or regrow annually. Therefore, sensitivity is assessed as ‘Low’. Overall, confidence is assessed as ‘Low’ due to evidence of variation and site-specific nature of competition between native kelps and both Undaria pinnatifida and Sargassum muticum.

Introduction of microbial pathogens

Benchmark. The introduction of relevant microbial pathogens or metazoan disease vectors to an area where they are currently not present (e.g. Martelia refringens and Bonamia, Avian influenza virus, viral Haemorrhagic Septicaemia virus). Further detail

Evidence

Laminarians may be infected by the microscopic brown alga Streblonema aecidioides. Infected algae show symptoms of Streblonema disease, i.e. alterations of the blade and stipe ranging from dark spots to heavy deformations and completely crippled thalli Infection can reduce growth rates of host algae (Peters & Scaffelke, 1996). The marine fungi Eurychasma spp can also infect early life stages of laminarians and Desmarestia viridis, however the effects of infection are unknown (Müller et al., 1999).

Sensitivity assessment. Due to a lack of conclusive evidence the sensitivity of this biotope cannot be assessed against this pressure.

Removal of target species

Benchmark. Removal of species targeted by fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

There has been recent commercial interest in Saccharina latissima as a consumable called “sea vegetables” (Birket et al., 1998). However, Saccharina latissima sporophytes are typically matured on ropes (Handå et al. 2013) and not directly extracted from the seabed, as with Laminaria hyperborea (Christie et al., 1998). No evidence has been found for commercial extraction of Saccorhiza polyschides or Desmarestia spp.. However, if the biotopes were subject to harvest, then a large propostion of the resisdent kelp population could be removed. . Thus evidence to assess the resistance of IR.HIR.KSed.Sac, IR.HIR.KSed.SlatSac, IR.HIR.KSed.DesFilR, IR.HIR.KSed.XKScrR to direct harvesting is limited. It has been assumed that if targeted harvesting were in operation it would remove >75% of sporophytes.

Sensitivity assessment. Resistance has been assessed as ‘None’, Resilience as ‘High’. Sensitivity has been assessed as ‘Medium’.

Removal of non-target species

Benchmark. Removal of features or incidental non-targeted catch (by-catch) through targeted fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

IR.HIR.KSed.Sac, IR.HIR.KSed.SlatSac, IR.HIR.KSed.DesFilR, IR.HIR.KSed.XKScrR Are characterised by a canopy of Saccorhiza polyschides, Saccharina latissima and Desmarestia spp. If the canopy were removed the red seaweeds understorey community may become bleached, and/or perish (Hawkins & Harkin, 1985), leading to further reductions in biodiversity. The biotope is however naturally periodically disturbed and as such would recover rapidly.

Sensitivity assessment. Resistance has been assessed as ‘None’, Resiliance as ‘High’. Sensitivity has been assessed as ‘Medium’.